1. Field of the Invention
The present invention relates to a resin-sealed electronic controller suitable as, for example, an on-vehicle electronic controller and a method of fabricating the same.
2. Description of the Related Art
In a control device for an automobile transmission, an integrated mechatronic product including an electronic controller provided inside the transmission is widely put into practical use. In the on-vehicle electronic controller, a circuit board formed by using a ceramic board is bonded to a thermally-conductive base plate serving as a heat diffuser plate. The entire body excluding a part of external connection terminals and the base plate is integrally molded with a thermally-curable resin.
For example, in an “electronic circuit device” described in Japanese Patent No. 4283514 (claim 1, paragraph [0268]) includes an electronic circuit assembly, a base plate, and lead terminals. The electronic circuit assembly includes electronic circuit elements including a semiconductor chip, and a circuit board on which the electronic circuit elements are mounted and a circuit pattern is formed. Onto the base plate, the electronic circuit assembly is bonded, and a flange portion is provided outside of an area in which the electronic circuit assembly is mounted. The lead terminals are electrically connected to the electronic circuit assembly and are made of a material having a larger linear expansion coefficient than that of the base plate.
The electronic circuit assembly, the base plate, and the lead terminals are molded at a time with a molding resin having a linear expansion coefficient substantially equal to that of the base plate except for a part of the flange portion and the lead terminals. The circuit board is a ceramic board. The base plate has a structure in which copper layers are formed on both surfaces of invar. The lead terminals are made of copper or a copper alloy material. A thickness center line of the molding resin in a vertical direction is approximately identical with a thickness center line of the circuit board.
According to the electronic circuit device described above, an inexpensive electronic circuit device for automobile without boundary separation between the molding resin, and the circuit board, the base plate and a lead frame or a resin crack due to a thermal stress can be realized.
However, the above-mentioned electronic circuit device has the following configuration. Specifically, the electronic circuit elements and the lead terminals are mounted on one surface of the circuit board, whereas the base plate is bonded to the other surface of the circuit board. Then, the electronic circuit elements, the lead terminals, the circuit board, and the base plate are integrally molded with the molding resin. At the same time, the thickness center line of the molding material after the molding is made substantially identical with the thickness center line of the circuit board.
Therefore, if electronic circuit components include a component having a large height, there are problems in that the circuit board cannot be bonded and an unnecessary molding resin undesirably adheres to a non-bonded surface of the base plate to be an excess thickness.
Moreover, one entire surface of the circuit board is bonded to the base plate. Therefore, the circuit board is a one-sided board having the other surface on which the electronic circuit elements and the lead terminals are mounded in a concentrated manner. Thus, there is a further problem that an increased area of a wiring board is required to ensure a mounting area for the circuit components.
Further, there is a further problem in that separation from molded outer covering material portions, which occurs with repeated changes in temperature due to a difference in linear expansion coefficient, is likely to occur if the wiring board has a large area.